riscv: cleanup svpbmt cpufeature probing

For better readability (and compile time coverage) use IS_ENABLED
instead of ifdef and drop the new unneeded switch statement.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20220905111027.2463297-2-heiko@sntech.deSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/cpufeature.c

@@ -253,16 +253,13 @@ void __init riscv_fill_hwcap(void)
 #ifdef CONFIG_RISCV_ALTERNATIVE
 static bool __init_or_module cpufeature_probe_svpbmt(unsigned int stage)
 {
-#ifdef CONFIG_RISCV_ISA_SVPBMT
-	switch (stage) {
-	case RISCV_ALTERNATIVES_EARLY_BOOT:
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_SVPBMT))
 		return false;
-	default:
-		return riscv_isa_extension_available(NULL, SVPBMT);
-	}
-#endif
 
-	return false;
+	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
+		return false;
+
+	return riscv_isa_extension_available(NULL, SVPBMT);
 }
 
 static bool __init_or_module cpufeature_probe_zicbom(unsigned int stage)